Why does my trigger and pull request NOT work in TeamCity?

we have tried to add a trigger and pull request feature in our building type. When a merge request in GitLab is opened, it will automatically trigger one building. We are using the Pull Request feature.

We have added the followed codes in our Build Types, but when we pushed some changes to the feature branch and open merge requests in Gitlab repo, it does not trigger the building. Or it performs quite weird, when we open MR-1, it does not trigger the building. Then if we open MR-2, it will trigger the MR-1 buildings

myBuildType: BuildType {
 ......
 
 features {
 
 val targetBranch = """
                    +:refs/heads/master
                    """.trimIndent()
    pullRequests {
        vcsRootExtId = "${DslContext.settingsRoot.id}"

        provider = gitlab {
            authType = token {
                token = MY_TOKEN
            }
            filterTargetBranch = targetBranch
            ignoreDrafts = true
        }
    }
 
 }
 
 val trigger = DslContext.getParameter("trigger", "false") == "true"
 if (trigger) {
        triggers {
            vcs {
                triggerRules = "+:."
                branchFilter = """
                +:merge-requests/*
                +:refs/merge-requests/*
                +:master
                """.trimIndent()
            }
        }
    }
    
}

In the project in TeamCity, we set up the VCS root as followed:

Default branch: refs/heads/my_build_settings_branch
Branch specification: +:my_build_settings_branch
                      

Any advice? Thanks